Methods of non-destructive residual stress measurement using barkhausen noise and use of such methods

ABSTRACT

A method for determining residual stress in a selectively hardened parts including an unhardened region adjacent to a hardened region is provided. The method includes obtaining a Barkhausen Noise (BN) value for the unhardened region and selecting a corresponding absolute residual stress value from a look-up table. The selected absolute residual stress value accurately estimates the absolute residual stress in the hardened region of the selectively hardened part. In variations of the method the unhardened region is surrounded by the hardened region, the hardened region is a laser hardened region and the unhardened region is not laser hardened.

FIELD

The present disclosure relates to non-destructive evaluation (NDE) ofmetallic parts, and particularly to NDE of metallic parts usingBarkhausen Noise.

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

The measurement of stress at or near a surface of a metallic part (alsoknown as “residual stress”) may be important to determine if the surfaceregion is in a compressive stress state, a tensile stress state, or aneutral stress state. For example, a metallic surface under compressivestress is known to have enhanced fatigue and/or galling resistancecompared to a similar surface under tensile stress. As such, surfaces ofmetallic parts may be heat treated (e.g., heated to an elevatedtemperature and cooled) in order to put the surfaces in a compressivestate.

The absolute residual stress at and near the surface of a metallic partis typically measured using an x-ray diffraction (XRD) technique.Particularly, the part must be sectioned, a surface is scanned via XRD,chemically etched to remove a prescribed depth, scanned again via XRD,etched again, scanned again via XRD, etc., until a series of XRD scansas a function of depth within the surface of the metallic part areobtained. Also, the absolute residual stress, both hoop and axial, ateach depth can be calculated from the series of XRD scans. However, theXRD scanning technique is time consuming, expensive, and destructive tothe metallic part (i.e., it is a destructive measurement technique).

Barkhausen Noise (BN), derived from the “Barkhausen effect”, is onetechnique that has been investigated for non-destructive measurement ofresidual stress in surface regions of metallic parts. The BN techniqueis based on or results from “noise” that occurs when a magnetic fieldwithin a ferromagnetic material changes, i.e., when the magnetic fieldmoves within the ferromagnetic material. While the BN technique does notprovide measurements of absolute residual stress, the quantity ormagnitude of the BN is related to material inhomogeneities (e.g.impurities, crystal dislocations, voids) and the residual stress withinthe measured region. Accordingly, attempts have been made to correlateBN readings with absolute residual stress values obtained with the XRDscanning technique. However, BN is relatively insensitive to compressiveresidual stress and has only been useful for determining when a surfaceregion changes from a compressive stress state to a neutral stress stateor tensile stress state.

The present disclosure addresses the issues of detecting, measuring, andquantifying compressive residual stress in materials using BNtechnology.

SUMMARY

In one form of the present disclosure, a method for determining residualstress in a selectively hardened part comprising an unhardened regionadjacent to a hardened region is provided. The method comprisesobtaining a Barkhausen Noise (BN) response for the unhardened region andselecting an X-ray diffraction (XRD) residual stress value as a functionof the BN response from a look-up table. Also, the selected XRD residualstress value accurately estimates the residual stress in the hardenedregion of the selectively hardened part.

In some aspects of the present disclosure, the unhardened region is atleast partially surrounded by the hardened region. The hardened regionmay be a laser hardened region, the unhardened region may not be laserhardened and the selectively hardened part may be a crankshaft, acamshaft, or a gear. However, the method for determining residual stressin accordance with the teachings of the present disclosure may be usedon any part with an unhardened region surrounded by a hardened. In oneaspect of the present disclosure, the selectively hardened part is acrankshaft formed from a steel alloy, the hardened region is a pinjournal surface of the crankshaft, and the unhardened region is a pinoil hole. The pin journal surface may be laser hardened except for theregion surrounding the pin oil hole, and the laser hardened pin journalsurface may comprise a martensitic microstructure and the unhardenedregion surrounding the pin oil hole may comprise a ferriticmicrostructure.

In some aspects of the present disclosure, the laser hardened region isin a first stress state and the unhardened region is in a second stressstate that is more positive than the first stress state. For example,the laser hardened region may be in a compressive stress state and theunhardened region may be in a neutral stress state and/or a tensilestress state. Also, the laser hardened region may have a first hardnessand the unhardened region may have a second hardness that is less thanthe first hardness.

The look-up table may include a plurality of XRD residual stress valuesfor a plurality of hardened regions within a plurality of selectivelyhardened parts, and a plurality of BN responses for a plurality ofunhardened regions within the plurality of selectively hardened parts.In some aspects of the present disclosure, the plurality of XRD residualstress values and the plurality of BN responses of each generally obey alinear relationship. In one aspect of the present disclosure, theplurality of XRD residual stress values obeys a first linearrelationship and the plurality of BN responses obeys a second linearrelationship that is different than the first linear relationship.

In another form of the present disclosure, a method of determiningresidual stress of a hardened region in a selectively hardened partincludes creating a look-up table comprising XRD residual stress valuesand BN responses from a plurality of selectively hardened parts. The XRDresidual stress values include XRD residual stress measurements from aplurality of hardened regions of the plurality of selectively hardenedparts with a range of residual stresses. The BN responses include BNreadings from a plurality of unhardened regions of the plurality ofselectively hardened parts with a range of residual stresses. Theunhardened region of each of the plurality of selectively hardened partsis adjacent to the hardened region such that a residual stress of theunhardened region is a function of a residual stress of the hardenedregion. The method also includes scanning an unhardened region of aselectively hardened part with a BN scanner, obtaining a BN response,and selecting an XRD residual stress value from the look-up tablecorresponding to the BN response. The selected XRD residual stress valueaccurately estimates the residual stress in the hardened region of theselectively hardened part thereby providing a non-destructive evaluationof the residual stress in the hardened region.

In yet another form of the present disclosure, a system for measuringresidual stress is provided. The system includes a BN scanning systemconfigured to scan an unhardened region of a selectively hardened partand obtain a BN response for the unhardened region. A look-up table maybe included in the system and the look-up table may comprise a pluralityof XRD residual stress values for a plurality of hardened regions from aplurality of selectively hardened parts and a plurality of BN responsesfor a plurality of unhardened regions from the plurality of selectivelyhardened parts. The plurality of XRD residual stress values may includea progression of linearly increasing residual stress values and theplurality of BN response may include a progression of linearlyincreasing BN responses. The unhardened region of each of the pluralityof selectively hardened parts may be adjacent to the hardened region ofeach of the plurality of selectively hardened parts such that a residualstress of the unhardened region is a function of a residual stress ofthe hardened region. The system may include a microprocessor configuredto receive a BN response for an unhardened region of the selectivelyhardened part from the BN scanning system and select an XRD residualstress value from the look-up table as a function of the BN response.The selected XRD residual stress value accurately estimates a residualstress of a hardened region of the selectively hardened part.

Further areas of applicability will become apparent from the descriptionprovided herein. It should be understood that the description andspecific examples are intended for purposes of illustration only and arenot intended to limit the scope of the present disclosure.

DRAWINGS

In order that the disclosure may be well understood, there will now bedescribed various forms thereof, given by way of example, referencebeing made to the accompanying drawings, in which:

FIG. 1 schematically depicts a selectively hardened part with a hardenedregion being scanned with a Barkhausen Noise (BN) scanner;

FIGS. 2A and 2B graphically depict an X-ray diffraction (XRD) residualstress and BN response analysis of the part in FIG. 1;

FIG. 3 schematically depicts a selectively hardened part an unhardenedregion being scanned with a BN scanner;

FIGS. 4A and 4B graphically depict an XRD residual stress and BNresponse analysis of the part in FIG. 3 according to the teachings ofthe present disclosure;

FIG. 5A schematically depicts a crankshaft with an oil hole in a pin ofthe crankshaft;

FIG. 5B schematically depicts an enlarged view of the oil hole in FIG.5A;

FIG. 6 schematically depicts a method of determining residual stress ina selectively hardened part comprising an unhardened region adjacent toa hardened region according to the teachings of the present disclosure;

FIG. 7 schematically depicts a method of determining residual stress ofa hardened region in a selectively hardened part according to theteachings of the present disclosure; and

FIG. 8 schematically depicts a residual stress measurement systemaccording to the teachings of the present disclosure.

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of the present disclosure in any way.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is notintended to limit the present disclosure, application, or uses. Itshould be understood that throughout the drawings, correspondingreference numerals indicate like or corresponding parts and features.

Referring to FIG. 1, a hardened part 10 with a hardened region 12 isschematically depicted. A BN scanner 16 is configured to scan and obtaina BN response (also referred to herein as “BN reading” and “BN value”)from the hardened region 12.

Referring now to FIGS. 2A and 2B, a graphical depiction of absolute hoopand axial residual stress values (also referred to herein simply as“hoop residual stress”, “axial residual stress” and “residual stress”),respectively, and corresponding BN responses, is shown. Particularly,FIG. 2A provides a comparison of absolute hoop residual stress obtainedvia XRD at uniform relevant depths and BN response for exactly the samehardened part 10 over a range of residual stresses between about −65 ksito about +136 ksi. Similarly, FIG. 2B provides a comparison of absoluteaxial residual stress obtained via XRD at uniform relevant depths and BNfor exactly the same hardened part 10 over a range of residual stressesbetween about −80 ksi to about +130 ksi. As shown in FIGS. 2A and 2B,the BN response has a generally zero slope and is non-linear relative tothe XRD residual stress values and thereby does not correlate with theabsolute residual stress. Accordingly, a correlation between BN responseand residual stress is not available, particularly since the BN responsefor compressive residual stress (e.g., values between 0 ksi and −60 ksiin FIG. 2A) does not change. A step function in BN response occurs oncea tensile stress condition is recognized, but again, the relationshipremains non-linear to XRD residual stress. FIGS. 2A and 2B illustratethe traditional challenge faced when trying to utilize BN as anon-destructive means to determine residual stress.

It should be understood that the XRD residual stress values graphicallydepicted in FIGS. 2A and 2B require a significant amount of time (e.g.,hours) to obtain and the XRD technique is not practical for measuringresidual stress on a production parts, particularly production partsproduced in large quantities. Accordingly, earlier studies haveattempted to compare BN responses from hardened regions with XRDresidual stress standards developed for the hardened regions. However,given the lack of correlation noted above between BN responses andcompressive residual stress values such comparisons have not providedsuitable non-destructive measurement of residual stress using BN.

Referring now to FIGS. 3, 4A and 4B, a selectively hardened part 20 isschematically depicted in FIG. 3 and look-up tables according to theteachings of the present disclosure are graphically depicted in FIGS. 4Aand 4B. The selectively hardened part 20 comprises a hardened region 22and an unhardened region 24 adjacent to the hardened region 22. As usedherein, the phrase “unhardened region” refers to a region of a part thathas not been hardened during hardening of a hardened region of the partand is in a tensile stress state, a neutral stress state or acombination of a tensile stress state and a neutral stress state (i.e.,a residual stress generally equal to or greater than 0 ksi). In someaspects of the present disclosure, the hardened region 22 of theselectively hardened part 20 is laser hardened (i.e., the hardenedregion 22 is a laser hardened region 22) and the unhardened region 24 isnot laser hardened. The unhardened region 24 may at least partiallysurrounded or enclosed within the hardened region 22 and the residualstress within the unhardened region 24 is a function of the residualstress in the adjacent hardened region 22. Particularly, and assumingthe unhardened region comprises a tensile residual stress, the greaterthe compressive residual stress in the adjacent hardened region 22, thelower (i.e., less positive) the tensile residual stress in theunhardened region 24. As used herein the phrase “more positive” refersto a residual stress that is greater than another residual stress (e.g.,a residual stress of −5 ksi is more positive than a residual stress of−10 ksi, and a residual stress of +10 ksi is more positive than aresidual stress of +5 ksi). Also, the phrase “less positive” as usedherein refers to a residual stress that is less than another residualstress (e.g., a residual stress of −10 ksi is less positive than aresidual stress of −5 ksi, and a residual stress of +5 ksi is lesspositive than a residual stress of +10 ksi).

Referring specifically to FIG. 4A, a plurality of hoop residual stressvalues obtained via XRD at uniform depths for a plurality of hardenedregions 22 is graphically depicted. The plurality of hoop residualstress values range from about −180 ksi to about +100 ksi. FIG. 4Bgraphically depicts a plurality of axial residual stress values obtainedvia XRD at uniform depths for the plurality of hardened regions 22. Theplurality of axial residual stress values range from about −90 ksi toabout +200 ksi. FIGS. 4A and 4B also graphically depict a plurality ofBN responses for the plurality of unhardened regions 24 positionedadjacent to the plurality of hardened regions 22 for which the XRD hoopand axial residual stress values were measured. The plurality of BNresponses in FIGS. 4A and 4B provide a progression from about 20 toabout 250. Accordingly, FIGS. 4A and 4B represent BN responses whenmonitoring the unhardened region 24 relative to XRD stress of thesurrounding hardened region 22. FIGS. 4A and 4B illustrate the value inthe proposed alternative approach as residual stress can be evaluatedwith correlation over both compressive and tensile stresses. The valueof such a method is recognized as proactive monitoring of stress can beperformed without destructive testing.

As shown in FIGS. 4A and 4B, the progression of residual stress valuesand BN responses each generally follow or obey a linear relationship.Accordingly, the BN responses for the plurality of unhardened regions 24may be correlated with the progression of hoop residual stress and axialresidual stress measured from the plurality of hardened regions 22. Thatis, an unhardened region 24 positioned adjacent a hardened region 22 aBN response that is proportional to the residual stress of the adjacenthardened region 22 and the residual stress of the hardened region 22 maybe determined from the BN response from the unhardened region 24. Thatis, the BN response of the unhardened region 24 is more sensitive toreport change and correlate with stress changes in the surroundinghardened region 22 since the unhardened region 24 is not undercompressive stress. Accordingly, a residual stress value may be selectedas a function of a BN response obtained from an unhardened region 22(e.g., selecting a residual stress value in FIG. 4A or 4B on the samevertical axis as the BN response) and the selected residual stress valueaccurately estimates the actual residual stress in a hardened region 22that is adjacent the unhardened region 24. As used herein, the phrase“accurately estimated” or “accurately estimates” refers to a selectedresidual stress value from a look-up table within at least +/−30% of anabsolute value measure via XRD. In some aspects of the presentdisclosure, a selected residual stress value is within at least +/−20%,e.g., within at least +/−10% of an absolute value measure via XRD. Asused herein, the phrase “look-up table” refers to a table, graph,equation, etc., that provides a residual stress value for a given BNresponse.

Referring now to FIGS. 5A and 5B, a crankshaft 30 with a selectivelyhardened pin 100 is schematically depicted. The selectively hardened pin100 may include a pin journal face 110 and a pin oil hole 112. The pinjournal face 110 may comprise a hardened region 111 and an unhardenedregion 114 adjacent the hardened region 111 and surrounding the oil hole112. In some aspects of the present disclosure, the pin journal face 110may be selectively hardened using laser hardening. That is, laserhardening may be used to heat the pin journal surface 110, except forthe unhardened region 114 surrounding the pin oil hole 112, followed bycooling of the pin journal surface 110.

It should be understood that laser hardening, and other selectivelyhardening techniques disclosed herein, increase the temperature of thesurface region to within a desired temperature range followed by coolingthe surface region such that the surface region is placed in acompressive stress state. However, the unhardened region 114, having notbeen heat treated, remains in a neutral state. While laser hardeningprovides enhanced temperature and spatial control for the heat treatmentof the journal surface 110, and other surfaces and parts disclosedherein, it should be understood that other heat treating techniques maybe used with the method taught in the present disclosure. Non-limitingheat treating techniques include induction heating, flame heating, gasor ion nitriding and the like.

In some aspects of the present disclosure, heat treating the hardenedregion 111, and other hardened regions described herein, results in aphase transformation of the surface region. For example, the selectivelyhardened pin 100 may be formed from a steel alloy, and heat treating thepin journal face 110 may result in the hardened region 111 having amartensitic microstructure. Also, the unhardened region 114, having notbeen heated treated similarly as the pin journal face 110, may have aferritic microstructure. As used herein, the phrase “martensiticmicrostructure” refers to a microstructure comprising at least 80 volumepercent (vol. %) martensite, for example at least 90 vol. % martensite,with bainite and retained austenite possibly present. Also, the phrase“ferritic microstructure” refers to a microstructure comprising ferriteand possibly pearlite with less than 10 vol. % martensite and/orbainite, for example less than 5% or less than bainite.

Still referring to FIGS. 5A and 5B, in some aspects of the presentdisclosure the method includes obtaining XRD hoop and/or axial residualstress for a plurality hardened regions 111 from a plurality of pins 100such that a hoop and/or axial residual stress profile is obtained (e.g.,see FIGS. 4A and 4B). The method also includes obtaining BN responsesfor the corresponding plurality of unhardened regions 114 from theplurality of pins 100 from which the XRD hoop and/or axial residualstress was obtained. It should be understood that the BN responses forthe unhardened regions 114 are proportional to the XRD hoop and/or axialresidual stress for the hardened regions 111 (e.g., see FIGS. 4A and4B). Accordingly, a correlation between the BN responses for theunhardened regions 114 and the XRD hoop and/or axial residual stress forthe hardened regions 111 may be provided and used to estimate theresidual stress in hardened regions 111 not subjected to XRD residualstress measurement. For example, after the correlation between theresidual stress and the BN response has been determined for the pinjournal surface 110, a BN response from an unhardened region 114 of apin 100 not analyzed via XRD may be used to estimate the residual stressin the hardened region 111 surrounding the unhardened region 114.

Referring now to FIG. 6, in one form of the present disclosure, a method40 for determining residual stress in a selectively hardened partcomprising an unhardened region adjacent to a hardened region isprovided. The method 40 includes obtaining a BN response from anunhardened region of the selectively hardened part at step 42. In someaspects of the present disclosure, the BN response is obtained byscanning the unhardened region of a selectively hardened part with a BNscanner. One non-limiting example of a BN scanner is a CrankScan 1000 BNScanner sold by American Stress Technologies located in Pittsburgh, Pa.After the BN response is obtained at step 42, a residual stress valuefor the hardened region is selected (e.g., using a plot as in FIGS. 4Aand/or 4B). As described above, the selected residual stress valueaccurately estimates the actual residual stress as measured via XRD forthe hardened region of the selectively hardened part.

Referring now to FIG. 7, in another form of the present disclosure, amethod 50 for determining residual stress in a selectively hardened partcomprising an unhardened region adjacent to a hardened region isprovided. The method 50 includes creating a look-up table comprisinghoop and/or axial residual stress values and BN responses from aplurality of selectively hardened parts at step 52. The look-up tablemay be created by obtaining XRD hoop and/or axial residual stresses andBN responses for a plurality of selectively hardened parts as describedabove such that an XRD hoop and/or axial residual stress profile and acorresponding BVN response profile are provided. At step 54 anunhardened region of a selectively hardened part is BN scanned and a BNresponse value is obtained. At step 56 a corresponding residual stressvalue is selected from the look-up table. It should be understood thatthe selected residual stress value accurately estimates the residualstress in the hardened region of the selectively hardened part.

Referring now to FIG. 8, in yet another form of the present disclosure,a system 60 for measuring residual stress is provided. The system 60comprises a BN scanning system 62 with a BN transmitter/receiver 64configured to scan an unhardened region of a selectively hardened part(e.g., a pin 100 of a crankshaft 30) and obtain a BN response for theunhardened region. As schematically depicted in FIG. 8, the BN scanningsystem 62 includes one or more controls 63, switches, etc., such thatthe BN transmitter/receiver 64 moves in the x- and y-directions and BNscans various portions of the selectively hardened part. Also, it shouldbe understood that the BN scanning system is operable to rotate theselectively hardened part about the x-axis shown in the figure. The BNtransmitter/receiver 64 is in communication with a microprocessor 66 andthe microprocessor 66 is in communication with a look-up table 68. Thelook-up table 68 that has a plurality of hoop and/or axial residualstress values from a plurality of hardened regions of a plurality ofselectively hardened parts and a plurality of BN responses from aplurality of unhardened regions of the plurality of selectively hardenedparts may be included.

Still referring to FIG. 8, the BN scanning system 60 BN scans anunhardened region of the selectively hardened part and obtains a BNresponse from the unhardened region. The microprocessor 66 receives theBN response and selects a corresponding residual stress value from thelook-up table 68 and provides the selected residual stress value to auser. The selected residual stress value accurately estimates theresidual stress in a hardened region that is adjacent to the unhardenedregion of the selectively hardened part. It should be understood thatthe microprocessor 66 and the look-up table 68 may be included in acomputer 69 which may or may not be part of the BN scanning system 62.That is, the computer 69 may be a separate component from the BNscanning system 62 and may include a software program 70 withinstructions that result in a comparison of the BN response from anunhardened region to values in the look-up table 68 and providing acorresponding residual stress value from the look-up table 68 to a user.

While FIG. 8 schematically depicts a crankshaft 30 being BN scanned withthe BN scanning system 62, it should be understood that BN scanningsystems that BN scan parts with flat surfaces comprising an unhardenedregion adjacent and/or surrounded by a hardened region are included inthe teachings of the present disclosure.

The description of the disclosure is merely exemplary in nature and,thus, variations that do not depart from the substance of the disclosureare intended to be within the scope of the disclosure. Such variationsare not to be regarded as a departure from the spirit and scope of thedisclosure.

What is claimed is:
 1. A method for determining residual stress in aselectively hardened part comprising an unhardened region adjacent to ahardened region, the method comprising: obtaining a Barkhausen Noise(BN) value for the unhardened region; selecting an X-ray diffraction(XRD) residual stress value as a function of the BN value from a look-uptable, wherein the selected XRD residual stress value accuratelyestimates the residual stress in the hardened region of the selectivelyhardened part.
 2. The method of claim 1, wherein the unhardened regionis surrounded by the hardened region.
 3. The method of claim 1, whereinthe hardened region is a laser hardened region and the unhardened regionis not laser hardened.
 4. The method of claim 3, wherein the laserhardened region is in a compressive stress state and the unhardenedregion is in a neutral stress state, a tensile stress state or acombination of a neutral stress state and a tensile stress state.
 5. Themethod of claim 3, wherein the laser hardened region is in a firststress state and the unhardened region is in a second stress state thatis more positive than the first stress state.
 6. The method of claim 3,wherein the laser hardened region comprises a first hardness and theunhardened region comprises a second hardness that is less than thefirst hardness.
 7. The method of claim 1, wherein the selectivelyhardened part is selected from the group consisting of a crankshaft, acamshaft, and a gear.
 8. The method of claim 1, wherein the selectivelyhardened part is a crankshaft, a pin journal surface or the crankshaftcomprises the hardened region, and the unhardened region surrounds a pinoil hole within the pin journal surface.
 9. The method of claim 8,wherein the pin journal surface is laser hardened except for theunhardened region surrounding the pin oil hole.
 10. The method of claim9, wherein the laser hardened pin journal surface comprises amartensitic microstructure and the unhardened region surrounding the pinoil hole comprises ferritic microstructure.
 11. The method of claim 1,wherein the look-up table comprises a plurality of XRD residual stressvalues for a plurality of hardened regions within a plurality ofselectively hardened parts and a plurality of BN values for a pluralityof unhardened regions within the plurality of selectively hardenedparts, wherein the plurality of XRD residual stress values and theplurality of BN values each generally obey a linear relationship.
 12. Amethod of determining residual stress of a hardened region in aselectively hardened part, the method comprising: creating a look-uptable comprising X-ray diffraction (XRD) residual stress values andBarkhausen Noise (BN) values from a plurality of selectively hardenedparts, wherein: the XRD residual stress values correspond to XRDresidual stress measurements of a plurality of hardened regions from aplurality of selectively hardened parts with a range of compressiveresidual stresses and the BN values correspond to BN responses of aplurality of unhardened regions from the plurality of selectivelyhardened parts with a range of neutral and tensile residual stresses;the unhardened region of each of the plurality of selectively hardenedparts is adjacent the hardened region such that a residual stress of theunhardened region is a function of a residual stress of the hardenedregion; scanning an unhardened region of a selectively hardened partwith a BN scanner and obtaining a BN response; and selecting an XRDresidual stress value from the look-up table corresponding to the BNresponse, wherein the selected XRD residual stress value accuratelyestimates the residual stress in the hardened region of the selectivelyhardened part.
 13. The method of claim 12, wherein the unhardened regionis surrounded by the hardened region.
 14. The method of claim 12,wherein the hardened region is a laser hardened region and theunhardened region is a unhardened region.
 15. The method of claim 12,wherein the selectively hardened part is selected from the groupconsisting of a crankshaft, a camshaft, and a gear.
 16. The method ofclaim 12, wherein the selectively hardened part is a crankshaft, thehardened region is a pin journal surface and the unhardened region is apin oil hole.
 17. A residual stress measurement system comprising: aBarkhausen Noise (BN) scanning system configured to scan an unhardenedregion of a selectively hardened part and obtain a BN value for theunhardened region; a look-up table comprising a plurality of BN valuesfor a plurality of unhardened regions with a range of residual stressesfor a plurality of selectively hardened parts and a plurality of X-raydiffraction (XRD) residual stress values for a plurality of hardenedregions with a range of residual stresses from the plurality ofselectively hardened parts, wherein the unhardened region of each of theplurality of selectively hardened parts is adjacent to the hardenedregion such that a residual stress of the unhardened region is afunction of a residual stress of the hardened region; and amicroprocessor configured to receive the BN value for the unhardenedregion of the selectively hardened part from the BN scanning system andselect an XRD residual stress value as a function of the BN value fromthe look-up table, wherein the selected XRD residual stress valueaccurately estimates a residual stress of a hardened region of theselectively hardened part.
 18. The system of claim 17, wherein the BNvalues in the look-up table are from a plurality of unhardened regionssurrounded by the plurality of hardened regions such that eachunhardened region is surrounded by a hardened region.
 19. The system ofclaim 17, wherein the BN values and the XRD residual stress values eachobey a linear relationship.
 20. The system of claim 17, wherein theselectively hardened part is selected from the group consisting of acrankshaft, a camshaft, and a gear.